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Relationship between key cephalometric parameters and tooth tip and torque

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Relationship between key cephalometric parameters and tooth tip and torque

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Content RELATIONSHIP BETWEEN KEY CEPHALOMETRIC PARAMETERS (ANB, SN-GOGN)

AND TOOTH TIP AND TORQUE

by

Garrett Fong

_____________________________________________________________________________

A Thesis Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
(CRANIOFACIAL BIOLOGY)

May 2012

Copyright 2012 Garrett Fong
ii
DEDICATION

This thesis is dedicated to my family, friends, and instructors. To my family, you have been an
unwavering source of support for my entire life. You have always wanted the very best for me and
done everything possible to help me achieve my goals. I could not have asked for better role
models to emulate personally and professionally. Any success I am able to achieve is a direct
reflection of your love, support, and sacrifice. To my friends, I am honored to have such loyal,
caring, and generous people to call my friends. Your friendship has given me strength and
provided my life with the intangible balance necessary to continue working towards my professional
goals. To my instructors, your dedication to education and your students is greatly appreciated
and I would not be here without the cumulative efforts of each and every one of you.
iii
ACKNOWLEDGMENTS

I would like to express my gratitude to my research advisor, Dr. Hongsheng Tong. Your guidance
and vision with this project, preceding projects, and future projects is inspiring and very much
appreciated. I would also like to extend special thanks to my statistics advisor, Dr. Reyes Enciso.
Your guidance in analyzing such a large amount of data was invaluable.
iv
TABLE OF CONTENTS

Dedication ii

Acknowledgments iii

List of Tables vi

Abstract vii

Chapter 1: Introduction 1

Chapter 2: Materials & Methods 6
I. Case Selection Criteria 6
II. Generating 2D Lateral Cephalometric Films From 3D CBCT X-Rays 7
III. Cephalometric Tracing Calibration Phase and Digitization of Cases 8
IV. Data From Previous Study On Tip And Torque Using The Same Patient
Population 9
V. Statistical Analysis Comparing Cephalometric Parameters And Previously
Studied Tip And Torque Values 10

Chapter 3: Results 11
I. Patient Sample 11
II. Correlation Studies 12
Effect Of ANB On Faciolingual Inclination 12
Effect Of SN-GoGn On Faciolingual Inclination 13
Effect Of ANB On Mesiodistal Angulation 14
Effect Of SN-GoGn On Mesiodistal Angulation 14

Chapter 4: Discussion 16
I. Case Selection 16
II. Digitization Calibration 17
III. Comparison To Previous Studies 18
Effect of SN - GoGn on Faciolingual Inclination 18
Effect of ANB on Faciolingual Inclination 21
Effect of ANB on Mesiodistal Angulation 23
Effect of SN - GoGn on Mesiodistal Angulation 24

v
IV. Clinical Implications 26
V. Future Studies 27

Chapter 5: Conclusion 29

References 31
vi
LIST OF TABLES

TABLE 1: Study Group Profile 11

TABLE 2: Torque X ANB; Torque X SN-GoGn 12

TABLE 3: Tip X ANB; Tip X SN-GoGn 14

vii
ABSTRACT

The purpose of this study was to determine the most accurate correlations between different
skeletal patterns and tooth inclination and angulation by using data purely from CBCT X-rays to
minimize inaccuracies inherent in previous studies based on traditional X-rays. After determining a
set of inclusion and exclusion criteria, 91 cases with “near normal” occlusion were selected. CBCT
X-rays were used to generate 2D lateral cephalometric head films with minimal amounts of noise
and distortion to maximize accuracy in landmark identification. ANB and SN-GoGn were chosen to
represent antero-posterior and vertical skeletal parameters, respectively. Data from Kwon’s
previous study on ideal tip/torque values was used to perform correlation studies with the
aforementioned cephalometric parameters. Labial crown torque for upper incisor, canine, and
premolar teeth were found to be positively correlated with an increase in mandibular plane angle (p
< 0.05). There was no indication of a significant correlation existing between upper molars and
mandibular plane angle. Mandibular plane angle was not shown to have a significant correlation
with faciolingual inclinations of upper molars or any lower teeth. ANB shared a negative correlation
with the torque of the maxillary first molar, and a positive correlation with each lower tooth (p <
0.05). There was a positive correlation between mesial tip of the lower canine and an increased
ANB value (p < 0.05). The clinical implication of this study is the importance in recognizing that
dental and skeletal characteristics are unique to each individual. Patents should not all be treated
in the same manner with the same objectives. Bracket prescriptions have been created according
to certain patient populations and are not intended for universal application without modifications.
viii
The orthodontist must focus on the individual needs for each patient and customize each case
through modified bracket positioning or wire bending as necessary.
1
CHAPTER 1: Introduction

Orthodontics is the specialty of dentistry dedicated to the diagnosis and treatment of
malocclusions, resulting from dental or craniofacial irregularities. Treatment goals consist of
achieving optimal occlusion, esthetics, and stability.
1

Significant contributions in the area of orthodontic occlusion were made by Edward Angle and
Lawrence Andrews. Angle, the “Father of modern orthodontics,” provided orthodontists with a
quintessential guideline for evaluating occlusion that is still used today. Prior to Angle, minimal
importance was placed on bite relationships and the main orthodontic objectives were to resolve
crowding and alignment issues. Angle’s molar inter-arch relationship classification system
revolved around the positioning of the upper first molars with respect to the lower first molars and
was an important first step towards understanding occlusion.
2
Ideally, the mesiobuccal cusp of the
upper first molar should occlude with the buccal groove of the lower first molar to yield a normal
occlusion. In addition, Angle was a pioneer in developing the initial contemporary fixed appliance
systems, which were designed with an emphasis on precisely positioning each tooth in different
dimensions. These included such systems as the E-arch, the Pin and Tube, the Ribbon Arch, and
ultimately the Edgewise appliance.

It was recognized that the molar relationship described by Angle was not the only requirement
necessary for an ideal occlusion. To further elucidate the subject, Andrews studied 120 untreated
orthodontic patients that had naturally occurring ideal occlusions. His research resulted in several
2
advancements for the orthodontic specialty. It validated the importance of Angle’s molar cusp-
groove concept, in addition to identifying 5 other factors that were key components to occlusion.
These six keys contribute individually and collectively to the total scheme of occlusion and
therefore are viewed as essential to successful orthodontic treatment.
3
Crown mesio-distal
angulation (tip) and crown labio-lingual inclination (torque) values were recognized to fall within a
narrow range with respect to each tooth. Based off his findings, Andrews realized that mechanical
problems encountered by the orthodontist could be greatly reduced if tip and torque prescriptions
were built into the bracket instead of the arch wire.
4

5

6
Thus he developed the pre-adjusted
Straight-Wire Appliance (SWA) with built-in dimensional and angulation prescriptions for each
tooth. This greatly reduced the need for 1st, 2nd, and 3rd order bends, allowing the orthodontist to
treat cases using virtually straight rectangular wires with minimal bends.

Continuing advancements in bracket systems and bracket placement have allowed orthodontists to
treat patients with less effort, greater efficiency, and finish cases at a higher quality.
7
It must be
noted that brackets with built in prescriptions are the most effective if the long axis and center point
of each crown can be identified accurately, and the brackets are placed precisely. If this does not
occur, the orthodontist must make bends in the archwire to compensate for inaccuracies. For
example, brackets vertically displaced greater than 0.4mm have been found to result in torque
changes ranging from 2 to 10 degrees depending on the tooth and patient.
8

In addition to identifying common dental features such as tooth inclination and angulation among
normals, it is critical to evaluate how these parameters are affected by the skeletal relationships of
3
the jaws in individuals that differ from the norm when customizing treatment plans and identifying
specific treatment objectives.

Broadbent & Hofrath introduced roentgenographic cephalometry to orthodontics as an integral
component of diagnosis and treatment planning. By plotting anatomic landmarks on lateral
headfilm tracings, orthodontists could derive measurements to help evaluate growth patterns and
dento-skeletal relationships of the craniofacial complex. The advent of this technology stimulated
clinicians such as Downs, Steiner, and Ricketts, to develop unique analyses, each of which utilized
specific landmarks and measurements to evaluate different craniofacial relationships. For
example, Steiner incorporated what he thought to be the most clinically meaningful landmarks and
measurements into an analysis that examined the skeleton, dentition, and soft tissues. Normal
values for each measurement were determined based on what was found in individuals with
normal occlusions. This served as a reference point for identify varying degrees of abnormal
craniofacial relationships in comparison to population norms.

Following the introduction of roentgenographic cephalometry and Andrews’ research on crown
angulation and inclination, multiple studies have utilized dental casts and traditional lateral
cephalometric head films to evaluate tip, torque, and their potential relationships with different
craniofacial parameters.

Ross compared faciolingual inclinations of central incisors and first molars on dental casts relative
to cephalometric measurements and vertical growth patterns. Isaacson found that a straight-wire
4
appliance can result in creating undesired moments when used to treat individuals with vertical
skeletal growth patterns that deviate from the norm.
9
Janson studied posterior teeth using dental
casts and found that individuals with a vertical growth pattern had significantly greater buccal
inclination of maxillary posterior teeth than those with a horizontal growth.
10

Despite its usefulness, traditional two-dimensional (2D) cephalometry is commonly criticized for
errors relating to inherent magnification, superimposition, and distortion of structures. These
issues are unavoidable when using 2D imaging technology to capture three-dimensional (3D)
structures. In addition, measuring ideal tip and torque values on dental casts may no longer be the
most accurate method. Andrews and others used only the long axis of the crown, not the entire
tooth, to evaluate crown angulation and inclination. This was previously the most practical and
effective method, because roots were not visible clinically, and radiographs were insufficient.
Panoramic radiographs suffer distortion due to combined distortions in vertical and horizontal
dimensions.
11
Subsequently, the technology is limited in its ability to assess angular
measurements of tooth inclinations.
12
Lateral cephalometric radiographs provide a convenient way
of viewing the long axis of the incisors, but do not provide much information on crown angulation
and inclination of other teeth for the aforementioned reasons of bilateral superimposition and
distortion.
13

With the advent of CBCT technology, it is now possible to minimize these errors and study the
craniofacial complex more accurately than ever before by not only evaluating structures in three
dimensions on a 1:1 scale, but also isolating desired anatomic landmarks with designated x-ray
5
slices. In addition, 3D X-ray technology offers the advantage of choosing precise viewing angles to
examine different teeth, in comparison to 2D X-ray technology which offers only a single fixed
viewing angle.

Recognizing the importance of studying the whole tooth (crown and root) with regards to tip and
torque, Kwon performed a follow up to Andrews’ classic study. Kwon used CBCT x-rays of 79 near
normal orthodontic patients to determine standards for the mesio-distal angulation and bucco-
lingual inclination for each tooth (crown and root) in three dimensional space.
14
Tsunori also used
3D CT scans to evaluate the relationship between facial type, mandibular body inclination and
buccolingual inclination of teeth. He found that posterior teeth were more lingually inclined in
patients with shorter facial types and less steeply inclined mandibular planes.
15
Okada found that
the buccolingual inclination of the mandibular incisor and second molar were influenced by
mandibular plane angle (tsunori ref 9).
16
In a recent study, Shewinvanakitkul developed a
technique to measure mandibular teeth inclinations using CT scans and evaluated correlations
between tooth torque and interdental width in untreated patients.
17

The goal of the current study is to determine the relationship between the most significant antero-
posterior (ANB) and vertical (SN-GoGn) skeletal cephalometric parameters and individual tooth tip
and torque in patients with near normal occlusion. While previous studies may share similar
objectives, this is the first study to use tip, torque, and cephalometric measurements derived from
3D CBCT X-rays in an effort to reduce error and provide the most accurate, reproducible
measurements possible.
6
CHAPTER 2: Materials and Methods

I. CASE SELECTION CRITERIA

During the period between April 2004 and October 2009, approximately 2000 CBCTs were taken
as part of patient initial orthodontic records. One hundred one “near normal” cases were selected
from this group in a similar screening process to the one used by Andrews. Qualifying patients
were considered to be “near normal” if they had no history of orthodontic treatment, good health,
well aligned arches with normal appearing teeth, no supernumerary teeth, a low decayed, missing,
filled tooth index numerical value, and close to normal molar, overbite and overjet relationships.
Photographic and X-Ray screening were used to evaluate these parameters. The complete
inclusion and exclusion criteria is listed below.
Photo Screening
1. Complete dentition (did not require 3rd molars to be present or 2nd molars to
be fully erupted)
2. Molar relationship ranging from ! step Class II to " step Class III
3. Overbite and Overjet between 0-5mm
4. Spacing less than 6mm
5. Crowding less than 4mm (limited to maximum of 3 teeth)
6. Rotation less than 15 degrees (limited to maximum of 3 teeth)
7. No dental crossbite (limited to no more than 1 tooth)
8. No apparent arch form asymmetry
7
X-Ray Screening
1. Generally parallel roots
2. No obvious skeletal asymmetry

II. GENERATING 2D LATERAL CEPHALOMETRIC FILMS FROM 3D CBCT X-RAYS

CBCT X-Rays were used to generate 2D lateral cephalometric head films using Dolphin Imaging.
Noise reduction was performed by eliminating unnecessary soft tissue elements and limiting the
field to include only one half of the craniofacial complex in the sagittal plane. Soft tissue elements
were removed by filtering out all voxels more radiolucent than bone so that only skeletal structures
and teeth above that threshold were visible. Each X-ray was oriented with the occlusal plane
perpendicular to the floor and then the craniofacial complex was divided in the sagittal plane down
the facial midline into right and left halves. Because the sample consisted of patients with near-
normal occlusion, we could assume symmetry of the craniofacial structures bilaterally.
Subsequently, the left half was removed and the right half was selected to be representative of the
craniofacial complex and used to generate the lateral cephalometric headfilm.

This produced a lateral cephalogram without distortion from superimpositions of bilateral structures
or magnification errors that allowed for accurate and easily reproducible tracings. A custom
analysis was created using Dolphin Imaging software to evaluate the cephalometric parameters
ANB and SN-GoGn.
8

III. CEPHALOMETRIC TRACING CALIBRATION PHASE AND DIGITIZATION OF CASES

A calibration phase was done at the beginning of the study to confirm that cephalometric landmark
identification could be reliably reproduced. A random number generator was used to select 10
cases for this calibration. Each of these cases was digitized once initially, and then re-digitized
again 7 days later. Cephalometric values for both sets of tracings were generated by Dolphin
Imaging Software according to our custom analysis. These measurements were then used to
perform intra-examiner correlation coefficients (ICC) tests to check for reliability. The ICC value for
each parameter was greater than 0.95. This confirmed the reliability of cephalometric landmark
identification and the remaining cases were digitized. After all cases were digitized, a second ICC
test was performed according to the same process as the first to confirm consistency of
measurements throughout the study. ICC values were again greater than 0.95. In the process of
tracing the lateral headfilms, it was necessary to exclude ten cases due to incomplete imagery.
For example, the original x-rays were cut off in areas that contained anatomic landmarks (nasion,
gonion, gnathion) necessary for our study. Subsequently a total number of ninety-one cases was
available for statistical analysis.

9
IV. DATA FROM PREVIOUS STUDY ON TIP AND TORQUE USING THE SAME PATIENT
POPULATION

A customized 3D analysis program developed by Dolphin Imaging enabled Kwon in a previous
study to digitize individual teeth in three dimensions and determine their ideal tip and torque
values. This data was collected from the same patient population available to the current study,
but the case selection criteria varied slightly. The objective of the previous study was to determine
tooth tip and torque in patients judged to be near-normal based on occlusion and cephalometric
parameters.

Because the current study was focused on evaluating whether varying skeletal relationships affect
the tip and torque of teeth, we selected patients with near-normal dental occlusion, but expanded
the inclusion criteria to accommodate cases with a wider range of skeletal cephalometric values.
These cases represented a wider distribution of vertical (SN-GoGn) and antero-posterior (ANB)
skeletal values, allowing a greater range to evaluate possible effects on tooth tip and torque. By
examining tip and torque in patients with abnormal cephalometric parameters, we were interested
in studying natural dental compensations for skeletal discrepancies.

10
V. STATISTICAL ANALYSIS COMPARING CEPHALOMETRIC PARAMETERS AND
PREVIOUSLY STUDIED TIP/TORQUE VALUES

The collected data was combined with tooth tip and torque data from Kwon’s study. It should be
noted that even though Kwon’s selection criteria excluded cases that did not have near-normal
cephalometric values, tip and torque data was still collected for all 101 patients.

All data was entered into a Microsoft Excel spreadsheet and later analyzed with Statistical Package
for Social Sciences (SPSS) version 16.0 software for Macintosh. A Kolmogorov-Smirnov normality
test was used to test our data for normality. Any data with a “Sig.” value greater than 0.05 was
considered to be normal. Normal data was analyzed for correlations using Pearson correlation
coefficients. If the data was non-parametric, Spearman correlation coefficients were used instead.

Because multiple comparisons were performed, the significance level was adjusted with a Dunn-
Bonferroni correction. The standard significance level of p < 0.05 was divided by the number of
independent tests(6) that were performed to yield an adjusted p value of 0.0083.

VI. INSTITUTIONAL REVIEW BOARD APPROVAL

This study was approved by the University of Southern California Institutional Review Board (IRB).
The IRB approval ID is #UP-12-00136.

11
CHAPTER 3: Results

I. PATIENT SAMPLE

TABLE 1: STUDY GROUP PROFILE

One hundred one cases initially qualified for our selection criteria based on their near-normal
occlusion. However, ten cases were later excluded due to incomplete radiographic data, resulting
in a total of ninety-one cases (N = 91) in the study group. Cases were evaluated in groups based
on vertical (SN-GoGn) and anteroposterior (ANB) skeletal parameters. They were then
subcategorized into low, average, and high value categories based on norms and standard
deviations. Although there was a wide range of values for each skeletal parameter, it was evident
that the sample did not possess an even distribution across categories.

12
II. CORRELATION STUDIES

TABLE 2: TORQUE X ANB; TORQUE X SN-GOGN

*L1 Torque values consisted of non-parametric data…correlations were performed with Spearman's coefficient instead
of Pearson's coefficient
**Measurements were highlighted in yellow if the p-value < 0.05. Dunn-Bonferroni adjusted p-value < 0.083

1. Effect of ANB on Faciolingual Inclination
ANB did not affect the torque of any maxillary tooth except that of the first molar, which shared a
negative correlation with the antero-posterior parameter. The torque of all lower teeth was affected
by ANB with a positive correlation being present for each tooth. Each of these correlations was
associated with a p-value of less than 0.05. However, it should be noted that the correlations for
13
the upper first molar did not meet the adjusted p-value of 0.083 demanded by the Dunn-Bonferroni
correction.

2. Effect of SN-GoGn on Faciolingual Inclination
There was a strong tendency towards a positive correlation between SN-GoGn and upper anterior
and posterior torque (except the upper first molar) with statistically significant correlations existing
for upper incisors, canines, and 1st premolars (p < 0.05). However, the correlation for the upper
lateral incisor was the only one to satisfy the adjusted Bonferroni p-value. The upper second
premolar had a p-value close to 0.05 (p = 0.070). Torque for the lower teeth was unaffected by
changes in the SN-GoGn skeletal parameter.

14
TABLE 3: TIP X ANB; TIP X SN-GOGN

1. Effect of ANB on Mesiodistal Angulation
ANB was not demonstrated to have any correlation with the mesiodistal angulation of any tooth
except for the mandibular canine. In the case of the lower canine, an increase in mesial tip was
correlated with an increase in ANB (p < 0.05), but it did not meet the adjusted Bonferroni p-value.

2. Effect of SN-GoGn on Mesiodistal Angulation
A correlation was present between SN_GoGn and the tip of maxillary teeth. There was a
tendency for an increasingly positive correlation from posterior to anterior teeth with statistically
significant correlations present for upper lateral incisor and canine mesial angulations (p < 0.05).
Significant correlations were also demonstrated in lower canine and first premolar tip values (p <
15
0.05). However, only the upper lateral incisor correlation met the requirements for the adjusted
Bonferroni p-value (p = 0.003)

16
CHAPTER 4: Discussion

I. CASE SELECTION

Selecting patients with near normal occlusion was both an advantage and a limitation. It was
advantageous because it allowed us to investigate the relationship between variations in
craniofacial morphology and tooth tip and torque in some of mother nature’s best untreated
models. As Andrews recognized in his landmark study of normal occlusion, we have no better
example for emulation than nature’s best.
18
They provide invaluable information on natural dental
compensation for a diverse range of skeletal growth patterns. If we accept that stability is favored
in nature over instability according to the laws of thermodynamic stability, then the tooth
angulations and inclinations found in nature should represent their most stable positions
theoretically.
19
Subsequently in an effort to provide patients with the highest quality of care,
orthodontists should modify treatment objectives that follow nature’s guidelines to produce the
most stable end result for different patients.

The one size fits all philosophy is no longer appropriate to treat orthodontic patients. Straight wire
appliances that were developed based on normals in the population are sufficient to treat said
normals. However, when employing these same appliances with patients who fall outside of the
norm, the resulting mechanics may no longer produce the most desirable or stable results. By
studying the relationships between ANB, SN-GoGn, tooth tip and torque in patients with near-
17
normal occlusion, it was possible to determine trends indicating the most stable tooth positions for
patients of varying skeletal growth patterns.

The limitation of studying only patients with near-normal occlusion was that the majority of these
patients(approximately 75%) were measured to be in near-normal cephalometric value ranges
(Table 1). Subsequently, despite our sample providing a large overall range of values for SN-GoGn
and ANB, the distribution of cases outside of the norm was low in number. This allowed us to
examine correlations between SN-GoGn and tooth position, and ANB and tooth position.
However, because there were not enough cases representing the extreme ends of the range, it
was not possible to categorize subjects into high and low groups to perform statistical tests
(ANOVAs) and make comparisons like previous studies have done.

II. DIGITIZATION CALIBRATION

The calibration phase was used to determine the reliability of landmark identification during
digitization. ICC values were found to be greater than 0.95 for each measurement, confirming the
consistency of our tracings. When performing the calibration tracings, the same 2D generated
lateral cephalograms were used in each tracing. While this achieved the goal of demonstrating the
reliability of landmark identification, it would have been advantageous to re-generate a different
view of the 2D lateral cephalogram from the 3D CBCT to confirm the reliability of our methodology
as a whole. For example, by generating a second set of 2D lateral cephalograms for the
calibration phase by using the left sagittal segment of the craniofacial complex, instead of the right
18
as previously used, this would have also confirmed the assumption of symmetry between right and
left sides in our near-normal patient sample.

III. COMPARISON TO PREVIOUS STUDIES

1. Effect of SN - GoGn on Faciolingual Inclination (Table 2)
The current study shares similar objectives with previous studies. However, when comparing
studies, it is important to recognize that there are differences in case selection criteria and
methodologies. In separate studies, Ross and Janson investigated buccolingual inclinations in
subjects with varying facial vertical growth patterns.
9

10
Their measurement technique for
evaluating tooth inclination did not use the actual long axis of each tooth, but rather relied on
connecting a line between mesiobuccal and mesiolingual cusp tips. Tooth tip and torque values in
the current study were measured using the true long axis of each tooth, which was determined by a
line connecting the center of the crown and the center of the root in a three dimensional coordinate
system.
14
This provided a more accurate and reproducible evaluation of the long axis of each tooth
because it accounted for both crown and root anatomy, and eliminated potentially misleading
variations in surface contour and structure. Additionally, skeletal parameters were measured on
CBCT generated lateral headfilms, which were optimized for higher accuracy than traditional 2-D
cephalometrics.

Labial crown torque for upper incisor, canine, and premolar teeth were found to be positively
correlated with an increase in mandibular plane angle in our subjects (p < 0.05). This result was
19
supported by Ross who also found maxillary incisor faciolingual inclinations to increase in cases
with vertical growth patterns.
9
These findings support the trend of high angle patients having
narrower arch widths and crossbite tendencies.
20

21
Further studies from Fields investigating the
effect of respiratory patterns on vertical dentofacial morphology reveal the potential for mouth
breathing to alter the equilibrium in the craniofacial complex and favor jaw growth in a more vertical
direction. This could theoretically cause the mandible to rotate downward and backward, creating
increased pressure from stretched soft tissue, and ultimately leading to a constricted maxillary
dental arch.
22

23

From a dentoalveolar perspective, it would be a logical compensatory mechanism for maxillary
teeth in a narrow arch to have increased buccal crown torque in order to minimize crossbite
tendencies and also provide more space to alleviate crowding concerns. This could also explain
the longer functional lingual cusps observed by Isaacson.
24

Because of this, we expected to observe an increase in buccal crown torque extend through the
entire maxillary posterior. While an increased number of cases would probably make the nearly
significant (p = 0.07) upper second premolar correlation relationship into a significant one, there
was no indication of a significant correlation existing between upper molars and mandibular plane
angle. Due to clinical experience and the multiple studies that have confirmed a significant
relationship between upper molar faciolingual inclination and varying vertical growth patterns, we
believe that the lack of correlation found in this study is related to our near-normal patient sample,
and not representative of the actual relationship found in nature. Janson found maxillary posterior
20
teeth to have greater buccal inclinations in patients with vertical growth patterns.
10
Isaacson was in
agreement with Janson and concluded that high angle patients have posterior teeth with greater
buccal inclinations and longer functional lingual cusps.
24
Additional support comes from Tsunori’s
study that found upper posterior teeth in low angle patients were more lingually inclined.
15
Ross,
like the current study, did not find a correlation between mandibular plane angle and maxillary first
molar torque.
9
However, also like the current study, Ross’ patient sample was limited by a
relatively small number of subjects in the horizontal and vertical pattern groups and thus may not
be a true representation.

We also had expected that an increase in buccal crown inclination in the maxillary teeth would be
accompanied by a similar increase in lingual inclination of the mandibular teeth to compensate for
any crossbite tendencies. In a previous study by Hang, patients with low mandibular plane angles
were found to have wider arches, broader palates, and lingual crown inclinations of posterior
teeth.
20
However, the correlation tests revealed that the faciolingual inclinations of the lower teeth
were not influenced by mandibular plane angle in this study. A possible explanation for this can be
attributed to soft tissue pressure exerted on the mandibular teeth by the tongue. Tomes first
acknowledged the role of the surrounding soft tissues in determining the position of teeth. He
described an equilibrium theory where “the agency of the lips and tongue is that which determines
the position of the teeth.”
25
Graber further elaborated on the importance of recognizing the “role of
musculature in maintaining the stability of changes in tooth position when the orthodontic result is
not in balance with environmental forces and structures.
26
Myometric and electromyographic
research later determined that the tongue was able to exert greater pressure on the dentition than
21
the buccal musculature.
27

28
This does not mean that the tongue is more important than the lips or
cheeks in determining the position of the teeth, as equilibrium is a result of dynamics between
contractile and tonic forces, and hard and soft tissues.
29

However, it is clear that the tongue is capable of influencing tooth position. According to
equilibrium theory, moderate forces, from a habit like tongue thrusting, are not sufficient to cause a
change in tooth position. Rather, the resting tongue position, which provides sustained light
pressure against the teeth, is capable of influencing tooth positions in vertical and horizontal
directions.
23
Subsequently, in a high angle patient with narrow arches and a crossbite tendency,
the lower posterior teeth may attempt to incline lingually in a compensatory action, but the
muscular forces from the tongue in a buccal direction may prevent this from occurring.

2. Effect of ANB on Faciolingual Inclination (Table 2)
Buccolingual inclinations for all mandibular teeth were found to be positively correlated with more
positive ANB apical base relationships. However, no correlation was found between buccolingual
inclinations for the maxillary teeth and apical base relationship, except with regards to upper first
molar lingual crown torque. These results are consistent with previous studies.

The influence of the apical base relationship on tooth torque is well documented in the literature.
Steiner recognized the importance of “individualized treatment goals” because of the diversity in
craniofacial morphologies among patients. Patients could not all be treated to conventional norms
and still achieve ideal treatment outcomes. Subsequently, Steiner developed a set of acceptable
22
compromises for upper and lower incisor tooth positions with respect to varying relationships of the
apical bases. For example, an increase in the ANB angle can be compensated by an increase in
lower incisor proclination.
30

31

32
Lundstrom later examined the association between variations
between upper and lower apical bases, and upper and lower incisor inclinations. It was
demonstrated that larger positive ANB apical base relationships were compensated by proclination
of lower incisors, whereas retroclination was present in more negative apical base relationships.
33

These trends were also observed in the current study.

More recently, Arnett studied the affect of a wide range of ANB values on maxillary and mandibular
incisor inclination in untreated African Americans with normal occlusion. Arnett found ANB to have
a weak effect on maxillary incisor inclination, whereas a stronger correlation was demonstrated
between a more positive ANB angle, and incisor proclination.
34
This is similar to what was seen in
the current study. Upper incisor inclination was unaffected by varying ANB angles whereas lower
incisor proclination was significantly correlated with an increase in ANB. This may be due to the
fact that retroclination of upper incisors could cause issues with crowding by narrowing the dental
arch, whereas lower incisors are able to procline while forming a broader dental arch.

In addition to the upper incisors, no other maxillary tooth faciolingual inclinations showed a
significant correlation with ANB, except for the upper first molar. The torque of the upper first molar
was shown to be negatively correlated with an increase in ANB. This is consistent with previous
studies on Class II patients. As ANB increases, so does the Class II pattern. This results in a
wider part of the maxilla occluding with a narrower part of the mandible, which can lead to an
23
increased lingual inclination of the upper molar. Proffit stated that expansion is commonly needed
in Class II patients because their upper arch is usually “too narrow to accommodate the mandibular
arch when it comes forward into the correct relationship because the upper molars are tipped
lingually.”
23
Mosby also reinforced this concept in his text when warning of “hidden posterior
crossbites” that can occur in Class II patients.
35

36

3. Effect of ANB on Mesiodistal Angulation (Table 3)
Mesiodistal angulations for all teeth in both arches, except mandibular canines, were found to have
no correlation with the range of values for ANB. Mandibular canines exhibited a decrease in
mesial angulation in correlation with a less positive ANB value. This is consistent with what has
been found in the literature with regards to changes in crown angulation occurring as natural dental
compensation for sagittal skeletal discrepancies. The angulations of anterior teeth, particularly the
mesiodistal tip of canines, determine the amount of space those teeth occupy in the dental arch.
Subsequently, they have a direct relationship with incisor inclination and overjet.
3

37

38

39
This is
especially important in the dental compensation of a class III skeletal pattern, in which positive
anterior overjet is a main objective. Capelozza advocated modifying the original Andrews
appliance by increasing mesial angulation to maxillary canines and decreasing mesial tip of
mandibular canines for this purpose.
3 30
This would theoretically allow for an increase in upper
arch perimeter and a decrease in lower arch perimeter to help establish positive anterior overjet. In
a study by Maltagliati, only 27.9% of patients with normal occlusions exhibited correct dental crown
angulations according to the values established by Andrews.
40

3
This reinforced the importance in
recognizing that the optimum position for a tooth varies according to the individual dentofacial
24
complex. Azevedo examined canine angulation in untreated class I and class III individuals with
near normal occlusion and arrived at similar results to the current study. Class III individuals had
significantly less mesial angulation of the mandibular canines compared to individuals with a class I
skeletal pattern. In addition, they similarly found maxillary canine angulation to be unaffected
regardless of skeletal pattern.
41
This same trend was reported in a study by Busato evaluating the
compensation in mesiodistal axial inclinations of canines in Class II and Class III patients. They
found no statistically signifcant differences when comparing maxillary canines between groups, but
a more upright position tendency for mandibular canines was observed in the Angle Class III
sample.
42
It should be noted that the results of the current study reveal a significant correlation
between ANB and lower canine angulation. This can be interpreted in two ways - an increase in
ANB is correlated with an increase in mesial angulation; or a decrease in ANB is correlated with a
decrease in mesial angulation. Based on the aforementioned literature, it would appear that the
latter statement is more accurate, as the angulation of mandibular canines has only been found to
be altered in class III patients. In summary, mesiodistal tip of maxillary canines was not found to
be influenced by differences in ANB, and mesial angulation of mandibular canines is decreased in
patients with less positive ANB values.

4. Effect of SN - GoGn on Mesiodistal Angulation (Table 3)
When evaluating the effect of mandibular plane angle on mesiodistal tooth angulation, we
performed statistical analyses on both anterior and posterior teeth. However, we were primarily
concerned with correlations involving the canines because of their direct relationship with incisor
proclination in the dental compensation mechanism to obtain integrity of the occlusion. We found
25
that both maxillary and mandibular canines exhibited an increase in mesial angulation in correlation
with an increase in mandibular plane angle.

This trend partially agrees with previous studies by Sinclair and Casko.
43

44
Sinclair stated that in
his sample, patients with more obtuse gonial angles also had larger ANB values. This would
theoretically result in upper incisors being inclined lingually, and lower incisors being inclined
labially in natural dental compensation. Casko also found that when the mandibular plane is
steeper, incisors tend to be more upright in the maxilla and more protrusive in the mandible. In an
effort to obtain normal incisor relationships, it would be necessary for canines to be angulated in a
mesiodistal direction accordingly as seen in our study with mandibular canines.

However, maxillary canines in our study did not exhibit a more distal angulation as expected, and
in fact demonstrated a more mesial angulation in association with steeper mandibular planes.
Conflicting evidence is also present in the literature. Whereas Sinclair and Casko found that larger
mandibular planes were correlated with larger ANB values, Sanborn concluded that the gonial
angle is more obtuse and the lower border of the mandible is more steeply inclined in class III
patients. This resulted in labially inclined maxillary inisors, and lingually inclined mandibular
incisors.
45
If accurate, this would explain the mesially tipped upper canines, but not the mesially
tipped lower canines found in the current study. Because the findings in our study are in support of
two conflicting paradigms in the literature, it is not possible to come to a definitive conclusion on
this matter. Rather, it suggests that despite the close relationship that exists between vertical and
26
anteroposterior components of craniofacial development, this may be a multifactorial issue with
other factors involved.

IV. CLINICAL IMPLICATIONS

The clinical implication of this study is the importance in recognizing that dental and skeletal
characteristics are unique to each individual. Subsequently, patients should not all be treated in
the same manner with the same objectives. Steiner emphasized that the norms he established
were only to be used as a foundation for treatment planning, and that they must be modified
according to each individual.
32
It has been established that there is a large range of normal
variation in dental and skeletal relationships in people who have ideal occlusion.
44
It is evident that
compensatory tooth positioning occurs naturally to accommodate varying skeletal patterns. It is
our job as clinicians to recognize the best ways we can complement an individual’s dental and
skeletal relationship by either maintaining or enhancing these natural compensations. The straight
wire appliance has been one of the biggest contributions to the orthodontic treatment of patients. It
has allowed orthodontists to be more efficient and obtain higher quality results. However, it should
be recognized that bracket prescriptions have been created according to certain patient
populations and are not intended for universal application without modifications. The orthodontist
must focus on the individual needs for each patient and customize each case through modified
bracket positioning or wire bending as necessary.

27
V. FUTURE STUDIES

This study was the first to implement ideal tip and torque data, obtained by using the true long axis
of each tooth in Kwon’s previous 3D study, to explore correlations between different skeletal
growth patterns and tooth position.
14
Advances in three dimensional cone beam technology have
allowed for a more accurate and reproducible method for evaluating tooth angulation and
inclination, in addition to cephalometric x-ray landmark identification. This in turn allowed for more
accurate correlations to be established here than in previous studies. However, as mentioned
above with regards to case selection, our patient sample did not include an even distribution across
the range of values observed for the different skeletal growth patterns. Subsequently, it was not
possible to categorize subjects effectively into comparison groups. Only correlation studies could
be performed with our limited data set. Future studies would benefit from having an adequate
number of high angle cases to compare to low angle cases; in addition to a sufficient number of
high ANB cases to compare to low ANB cases. This would not only yield more accurate correlation
studies, but also provide more relevant data for clinicians to apply to patients that fit in varying
cephalometric ranges. Out of the patient population at the USC Graduate Orthodontics Program
that received cone beam CT scans during the period between 2000-2006, all cases that qualified
as having near-normal occlusion were included in this study. However, cone beam CT scans of
patients with near-normal occlusion should be available from other educational institutions that
were also taking 3D scans routinely as part of initial orthodontic records. Future studies can use
these CT scans and apply the same measurement technique used in Kwon’s study to analyze
tooth tip and torque. Then, cephalometric evaluation and comparison to tooth angulation and
28
inclination can be performed like in this study to gain an adequate number of cases for statistical
comparison. Age, ethnicity, gender, and transverse width of dental arches may also be interesting
factors for comparison.

29
CHAPTER 5: Conclusions

Labial crown torque for upper incisor, canine, and premolar teeth were positively correlated with an
increase in mandibular plane angle. This represents a compensatory mechanism for maxillary
teeth in a narrow arch to have increased buccal crown torque in order to minimize crossbite
tendencies.

There was no significant correlation existing between upper molars and mandibular plane angle.
This does not mean that one does not exist, but rather that this study failed to reveal them.
Multiple studies have in fact found a positive correlation existing between upper molar buccal
inclination and larger mandibular plane angles.

Buccolingual inclinations of the lower teeth were not influenced by mandibular plane angle in this
study, despite the compensatory benefits this might have in preventing crossbite. Pressure from
the tongue in a buccal direction could be responsible for this lack of lingual inclination.
Subsequently, it may not be stable for the orthodontist to add significant lingual crown torque to
mandibular teeth because the the position may not be favorable in terms of the soft tissue
equilibrium.

Buccolingual inclinations for all mandibular teeth were found to be positively correlated with more
positive ANB apical base relationships. However, no correlation was found between buccolingual
inclinations for the maxillary teeth and apical base relationship, except with regards to upper first
30
molar lingual crown torque. This is logical for the anterior teeth because they will procline to
establish normal incisor relationships. Buccal crown torque of mandibular posterior teeth may
increase for better occlusal contact with a broader section of the maxillary arch that is postured
forward.

A significant correlation between ANB and lower canine angulation was found. Mandibular canines
exhibited a decrease in mesial angulation in correlation with a less positive ANB value. This
should not be interpreted in the opposite direction, as previous studies indicate that an increase in
ANB is not necessarily correlated with an increase in mesial angulation.

Both maxillary and mandibular canines exhibited an increase in mesial angulation in correlation
with an increased mandibular plane angle. There is conflicting evidence in the literature to support
and deny both of these findings. Future studies need to be done to help clarify this issue further.
31
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Abstract (if available)

Abstract The purpose of this study was to determine the most accurate correlations between different skeletal patterns and tooth inclination and angulation by using data purely from CBCT X-rays to minimize inaccuracies inherent in previous studies based on traditional X-rays. After determining a set of inclusion and exclusion criteria, 91 cases with “near normal” occlusion were selected. CBCT X-rays were used to generate 2D lateral cephalometric head films with minimal amounts of noise and distortion to maximize accuracy in landmark identification. ANB and SN-GoGn were chosen to represent antero-posterior and vertical skeletal parameters, respectively. Data from Kwon’s previous study on ideal tip/torque values was used to perform correlation studies with the aforementioned cephalometric parameters. Labial crown torque for upper incisor, canine, and premolar teeth were found to be positively correlated with an increase in mandibular plane angle (p < 0.05). There was no indication of a significant correlation existing between upper molars and mandibular plane angle. Mandibular plane angle was not shown to have a significant correlation with faciolingual inclinations of upper molars or any lower teeth. ANB shared a negative correlation with the torque of the maxillary first molar, and a positive correlation with each lower tooth (p < 0.05). There was a positive correlation between mesial tip of the lower canine and an increased ANB value (p < 0.05). The clinical implication of this study is the importance in recognizing that dental and skeletal characteristics are unique to each individual. Patents should not all be treated in the same manner with the same objectives. Bracket prescriptions have been created according to certain patient populations and are not intended for universal application without modifications. The orthodontist must focus on the individual needs for each patient and customize each case through modified bracket positioning or wire bending as necessary.

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Asset Metadata

Creator Fong, Garrett S. (author)

Core Title Relationship between key cephalometric parameters and tooth tip and torque

School School of Dentistry

Degree Master of Science

Degree Program Craniofacial Biology

Publication Date 05/04/2012

Defense Date 03/09/2012

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag anb,angulation,cbct,cephalometric parameters,inclination,OAI-PMH Harvest,sn-gogn,tip,tooth,torque

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Sameshima, Glenn T. (committee chair), Enciso, Reyes (committee member), Paine, Michael L. (committee member), Tong, Hongsheng (committee member)

Creator Email gfong@usc.edu,gsfong.usc@gmail.com

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c3-31737

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